Urban merchants and Kshatriya oligarchs.
Brahman priests and monarchs.
Explanation:
Many of the people who supported Buddhism were urban merchants and Kshatriya oligarchs. These people actually thrived off of Buddhism, and with the increasing of trade, more people would turn to Buddhism, especially the merchants who would trade and travel consistently, spreading the religion even further.
Brahman priests and numerous monarchs actually thought of Buddhism as a threat. The Brahman priests saw Buddhism as an ultimate enemy, as the Hinduism that the Brahman priests practiced contradicted and went against the Buddhist views. With more people turning to Buddhism, this made Hinduism become more rare and less widespread.
